associations

Given :
Group hasMany Persons
but the relationship is independent (ie. Persons can exist without belonging to a Group), should the foreign key in the persons table (ie group_id) be set to 0 (or NULL) when deleting a group? If you do not, the person will try to belong to a group that does't exist.
The reason I ask is that this is...

Hello,
I've been looking for a generic way to deal with bidirectional associations and a way to handle the inverse updates in manual written Java code.
For those who don't know what I'm talking about, here is an example. Below it are my current results of (unsatisfying) solutions.
public class A {
public B getB();
public void ...

I have 2 classes with a LINQ association between them i.e.:
Table1: Table2:
ID ID
Name Description
ForiegnID
The association here is between Table1.ID -> Table2.ForiegnID
I need to be able to change the value of Table2.ForiegnID, however I can't and think it is because of the association (as wh...

I have to tables that have a many to many relationship. I have created the correct table codesecure_project_tst_definition and it works. I can join rows together by calling the codesecure_projects << method on a TstDefinition object. The problem is that for some reason active record wants to use Codesecure_project_id as the id value f...

I want to work with versioned ActiveRecord associations. E.g., I want to find the object that another object belongs_to as of a certain past date, or the one that it belonged to before that. Does there already exist a library subclassing Rails' ActiveRecord to provide versioned relations? Or some other Ruby library which provides persist...

So I have a User model that :has_many other models like Documents, Videos, Posts and the like. My question arises when I execute a "do" block from the User model like so:
has_many :posts do
def recent
find(:all, :order => 'created_at desc', :limit => 12)
end
end
This just lets me call something like user.posts.recent t...

I have a table that has a primary key that's an INT... I have another table, that has a foreignkey relationship to that first table, but it's a NULLABLE INT.
This is perfectly ok, and 100% acceptable to SQL... however LINQ to SQL is complaining about mismatched types ("int to Nullable[int]").
Error Message: Cannot create an association...

Hi,
I have a following SQL QUERY:
SELECT articles.name, articles.price, users.zipcode FROM articles INNER JOIN users ON users.id = articles.user_id WHERE vectors @@ to_tsquery('crime') ORDER BY articles.price ASC
And I Would like to write it inside of a find method from an ActiveRecord Class named Articles (Articles belongs_to user). B...

I was reading about self-referential has_many :through data situations today, because I'm trying to build a Rails application that uses them. I found this example situation on the Internet, and I have a question about it. Let me post this example code from this guy's blog:
create_table :animals do |t|
t.string :species
end
create_tabl...

When I have tables in my database that have PK/FK relationships (int) and when they are modeled by the Entity Framework designer everything seems as it should be. I can write the code below and everything seems like it's going to work fine as well but then when I run the code I get an error on the project.Status.StatusName saying the Ob...

Dear Stack,
Is it possible, using an Observer, to observe the creation of JOIN records? For example, you have a User Model that has_and_belongs_to_many Book Models. Is it possible to monitor books_users records as they are created or deleted or must I have a BookUser model to do this?
Example of what I want to observe:
User.books <<...

I have a user model which has multiple addresses. Now for my application in rails, address is not mandatory. So, if someone wants to create a user and enter the address after the user has been created, my application should allow that. My problem is, for Address model I have validations for Address Line 1, City and Postal Code. These fie...

I was wondering what the best way to model a relationship where an object is associated with exactly n objects of another class. I want to extend the has_one relationship to a specific value of n.
For example, a TopFiveMoviesList would belong to user and have exactly five movies. I would imagine that the underlying sql table would have...

I am working on a Django application which contains an Offer model. An Offer instance contains the pricing conditions and points to a product definition. The product model is actually a hierarchy (I have a Television model, a Camcorder model, etc.). So I would like the Offer model to contain a polymorphic (or "generic") association to...

Is there a way that I can get a list of the models that a particular model belongs to in Rails?
For example:
class Project < ActiveRecord::Base
has_one :status
...
end
class Task < ActiveRecord::Base
has_one :status
...
end
class Status < ActiveRecord::Base
belongs_to :project
belongs_to :task
# this is where I want to...

Right now I have a table called Campaigns that has many Hits, if I call say:
Campaign.find(30).hits
Which takes 4 seconds, or 4213 ms.
If I call this instead:
campaign = Campaign.find(30)
campaign.hits.count
Does it still load all of the hits, then count? Or does it see I am counting and avoids loading all of the hits? (Which is cur...

I've got a User model that has many Items. A Rating belongs to a User and an Item.
In the DB, I have set ratings.user_id to be not NULL.
when I am creating an Item, I would like to do this:
def create
current_user.items.create(params[:item]).ratings.create(params[:rating]
redirect_to items_path
end
However, this balks wi...